NASA Uses New Test To Determine If Voyager 1 Has Left Heliosphere To Enter Interstellar Space

If Voyager 1 is still inside heliosphere, scientists will observe a reversal in the direction of the solar magnetic field by the end of 2015. Photo: JPL/NASA

At a time when scientists are unclear about the current location of NASA’s Voyager 1, which began its journey toward interstellar space in 1990, a new study has proposed a test to determine whether the spacecraft has indeed left the heliosphere, a vast region of space surrounding the sun.

Although Voyager mission team members declared last year that Voyager 1 entered interstellar space in August 2012, some scientists remained unconvinced. The new study, which describes an alternate model for the interaction between the heliosphere and the interstellar medium, is expected to offer convincing information about Voyager 1's current whereabouts.

“It is the nature of the scientific process that alternative theories are developed in order to account for new observations,” Ed Stone of the California Institute of Technology in Pasadena and a scientist working with the Voyager project, said in a statement. “This paper differs from other models of the solar wind and the heliosphere and is among the new models that the Voyager team will be studying as more data are acquired by Voyager.”

Previous models that were used to conclude that Voyager 1 had entered interstellar space suggested that the density of interstellar wind outside the heliosphere is 40 times greater than the density of the solar wind inside. When scientists analyzed the observational data from the spacecraft, they found a plasma density that was 40 times higher, leading the scientists to conclude that Voyager 1 had indeed left the heliosphere and entered interstellar space sometime around Aug. 25, 2012.

However, other scientists questioned the conclusion saying that solar wind inside the heliosphere can be compressed to the point that its density could be as high as interstellar space, meaning Voyager 1 could still be inside the heliosphere.

According to the scientists working with the new study, if Voyager 1 is still inside the heliosphere, they will observe a reversal in the direction of the solar magnetic field sometime before the end of 2015. If that change does not occur, it will mean that Voyager 1 has already reached interstellar space.

“The proof is in the pudding,” George Gloeckler of the University of Michigan and lead author of the study said, in a statement. “This controversy will continue until it is resolved by measurements.”

Voyager 1 and Voyager 2 were launched 16 days apart in 1977. Both spacecrafts toured Jupiter, Saturn, Uranus and Neptune before kicking off for an interstellar mission in 1990.

Scientists estimate that both Voyager 1 and Voyager 2 will have enough electrical power to continue collecting data and communicating them back to Earth through 2020, and possibly, through 2025.